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1. Technical Field
The present invention relates in general to a photoelectric sensing array apparatus and a method of using it. More particularly, the present invention relates to position sensing of an opaque object located within a single or multi-dimensional array of infra red light beams.
2. Background Art
There are many known infra red (IR) sensor arrays used for position sensing by utilizing a row of infra red light emitting diode (LED) transmitters mounted on a rail, and a row of light sensing receivers (photo detectors) mounted on an opposite rail as illustrated in the diagram of FIG. 1. The position of an opaque object located between the transmitting array and the receiving array is determined by individually pulsing of the transmitter LED light sources while electronically sensing the response of the corresponding photo detectors.
The prior art array thus produces a multitude of invisible light beams, whereby corresponding sensors are blocked at the position where an opaque object is located. The center of the opaque object can be determined by electronically sensing current flow in each of the photo sensors, and then computing the center point of the region of blocked photo sensors.
Commonly this detection process is done in two axes simultaneously to create a two dimensional sensing grid such as found on a computer touch screen. Previous known sensor arrays of this type have the light emitting transmitters mounted on one rail and the photo detecting receivers mounted on the opposite rail. See U.S. Pat. Nos. 4,672,364; 4,841,141; 4,891, 508; 4,893,120; 4,904,857; 4,928,094; 5,162,783 and 5,579,035, which are each incorporated herein by reference.
There are serious drawbacks to this conventional method of photoelectric position sensing for some applications. The sensor array resolution is limited by the diameter of the largest optical component. In most applications, the LED transmitter dissipates much more power than the photo detector, and thereby requires a larger component package size. This configuration limits the resolution of the sensing array. For example, if the LED diameter is 0.25 inch and the photo detector diameter is 0.17 inch, the best attainable in-line array resolution, limited by the package size of the LED, is 4 points per inch. (See FIG. 2).
Conventional infra red light sensing arrays can give false readings or be blinded (photodetector saturation) by, for example, sunlight directed toward the receiving sensor rail. If the sensing is done across a horizontal plane, and if the IR light source is positioned on the bottom rail with the photo detectors on the top rail where they are typically shaded from the sunlight, the blinding problem can be somewhat ameliorated. The vertical plane however remains problematic, since throughout the course of a day, the sunlight can be directed toward either side of the array. Thus, blinding can still occur, and completely interfere with the desired operation of the array.
The design and production costs of multi-dimensional light beam arrays are high relative to other sensing technologies. For example, a two-dimensional touch-sensing array for a rectangular computer display typically requires four unique printed circuit cards. Thus, each one of the four circuits requires separate design and development, as well as production costs for assembling the circuits to the array, since each requires separate manufacturing techniques.
Thus, it would be highly advantageous to have a new and improved light sensing array which is relatively less expensive to manufacture, and which can be utilized at all times, even in direct sunlight. It would also be desirable to have a sensor array with a minimum or at least a greatly reduced number of different unique component assemblies to minimize or greatly reduce design time and reduce manufacturing costs.
It is, therefore, the principal object of the present invention to provide a new and improved photoelectric sensing array apparatus and method to increase the resolution of the array.
It is another object of the present invention to provide such a new and improved photoelectric sensing array apparatus and method, wherein the sensing array apparatus can still function even under certain extreme error conditions such as photo detector saturation caused by direct sunlight exposure.
It is yet another object of the present invention to provide such a new and improved photoelectric sensing array apparatus and method, wherein the array apparatus has a substantially reduced design and manufacturing cost.
Briefly, in accordance with the present invention, there is provided a new and improved photoelectric sensing array apparatus and method, which enable a sensing array to be constructed at a relatively low cost at improved resolution, and be able to function even under certain extreme error conditions such as photoelectric saturation caused by direct sunlight exposure.
A photoelectric sensor array apparatus and method, relates to at least two photoelectric rail elements each having alternating light emitting diode transmitters and photo detecting receivers. The array produces a plurality of light devices with corresponding sensors, whereby the light beams are blocked in the region where an opaque object is located. Each rail contains both transmitters and receivers so that control circuits for the transmitters and receivers are substantially identical and mounted on opposite sides of the array apparatus, to provide a more compact unit of higher resolution and to reduce the design and manufacturing costs. Such construction and method enable the sensing array apparatus to function in direct sunlight or other such photoelectric saturation conditions, which would otherwise blind conventional light sensitive sensor arrays.